This invention relates to an alloy that is suitable for coating orifice plates used with ink-jet pens to make the surface of the orifice plates non-wetting. More particularly, this invention relates to a precious metal-polymer alloy and orifice plates coated with the alloy. A non-wetting surface of an orifice plate minimizes puddling of ink in areas around orifices on the orifice plate and thus improves the print quality achievable with the orifice plate.
A prior art ink jet printer typically includes a printing cartridge or ink-jet pen in which small droplets of ink are formed and ejected toward a printing medium. Such an ink-jet pen includes-an orifice plate having very small nozzles or orifices through which the ink droplets are ejected. Adjacent to the orifices inside the ink-jet pen are ink chambers, where ink is stored prior to ejection.
Ejection of an ink droplet through an orifice may be accomplished by an associated drop ejection system. This drop ejection system is responsible for supplying ink to the ink chamber and quickly heating a volume of ink within the ink chamber on demand. The rapid expansion of ink vapor forces a drop of ink through the orifice. This process is called xe2x80x9cfiring.xe2x80x9d The ink in the chamber may be heated with a transducer, such as, a resistor that is aligned adjacent to the orifice.
Whenever an ink drop is ejected through an orifice, a trailing portion or xe2x80x9ctailxe2x80x9d of ink moves with the drop. A small amount of the ink tail may separate and land on the outer surface of the orifice plate as an ink droplet. Due to this separating of the ink tail, some of the ink that is ejected through the orifice does not reach the printing medium (such as paper), and instead collects on the outer surface of the orifice plate facing the printing medium. Some of this residual ink accumulates or puddles adjacent to the edge of the orifice. This puddle of residual ink may alter the trajectory of the subsequently ejected drops to cause an effect commonly known to those in the art as ink spray. Ink spray reduces the quality of a printed image.
Residual ink on the outer surface of the orifice plate also tends to trap stray particles, such as paper fibers. The fibers may be held by the ink near the orifice to partially block the orifice and interfere with ink drop ejections. Further, residual ink on the outer surface of the orifice plate may collect near the orifice into a thin sheet that is in fluid communication with ink stored in an ink chamber that is adjacent to the orifice. As a result, a continuous ink path between the ink chamber and the outer surface of the orifice plate may be formed. This path promotes ink leakage through the orifice. The prior art orifice plate of nickel or nickel coated with gold is susceptible to such puddling of ink. Accordingly, the outer surface of an ink-jet pen orifice plate should preferably be designed so that ink does not puddle in the vicinity of the orifice or accumulate on the orifice plate in an amount that traps fibers and facilitates leakage as mentioned above.
In the prior art, different methods using materials which are less wettable than gold have been used to address this ink puddling problem. In one of these methods, selected portions of the orifice plate outer surfaces are formed to have wetting and non-wetting surface characteristics for minimizing puddling to reduce spray. Specifically, an outside surface portion immediately surrounding the orifice edge is coated with a non-wetting fluorocarbon polymer such as that manufactured under the trademark Teflon by DuPont. This non-wetting surface causes any residual ink droplets to bead on that surface away from the edge of the orifice so that the residual ink does not interfere or come into contact with the drops that are later ejected from the orifice.
This method works but suffers a disadvantage. The process that is used to coat the polymer can only deposit a relatively thin layer (less than 1 micron) of the polymer material on the orifice plate. This thin layer of polymer material does not last. In use, this layer of polymer material wears off and puddling will again occur on the surface surrounding the edge of the orifice.
In another method experimented, orifice plates are coated with a layer of nickel-Teflon alloy up to several microns thick using an electroless deposition process. The performances of the ink-jet pens with such a coating exhibit better non-wetting characteristics than those with gold-plated orifice plates. Puddling is reduced and spray is almost eliminated in these ink-jet pens. However, these orifice plates also suffer a disadvantage. The nickel in the nickel-Teflon alloy reacts with the ink to cause the orifice plate to delaminate from a barrier layer of an ink-jet pen. As a result of this delamination, the life of an ink-jet pen is reduced.
The prior art therefore creates the need for an improved alloy and an orifice plate coated with the alloy that makes it less susceptible to the problem of ink puddling and at the same time more prone to a longer operational life than nickel-Teflon coated orifice plates.
According to one aspect of the present invention, an alloy that is suitable for coating a nickel orifice plate of an ink-jet printhead plate is made up of a precious metal and a polymer material. This precious-metal-polymer alloy allows the orifice plate to adhere to an intermediate layer of the ink-jet printhead and improves the non-wetting characteristics of the nickel orifice plate. According to one embodiment, the precious metal is gold and the polymer is Teflon.
According to another aspect of the present invention, an electrodeposition solution for electroplating the precious metal-polymer alloy has a carrier of ions of a precious metal, an acid buffer for maintaining the pH of the solution to be in the range of 2 to 4, suitable conducting salts to improve the conductivity of the electrodeposition solution and a dispersion of Teflon particles.
According to yet another aspect of the present invention, an orifice plate for an ink-jet pen has a plate that has an inner surface and an outer surface. The orifice plate has an orifice that extends through the plate between the inner surface and outer surface. At least a portion of the outer surface surrounding the orifice is coated with the precious metal-polymer alloy.